Re: (ET) Solid state controls

["Christopher Meier" <mr23 mn rr com>]

> If you want to go all out, you could make something like Lee Hart's
> Battery Balancer (as described on the EV list). This uses a
> microprocessor and small relays to monitor the voltage of each battery
> and then shuttle extra power to whichever battery is the lowest. You
> could add programming to display any information about the batteries you
> might like. However... that might be overkill for the application.

Lee's Balancer is overkill for the tractor; it's meant for higher voltage
series strings, so the parts cost alone is pretty high.  And it's a
significant
project as it doesn't include production software, it's an experiment in
progress.  The current draw of the drive and attachments on our ET's
doesn't unbalance our packs, it's the lights and lift that do most of the
damage.  A much cheaper route would be to switch the lights to 36v
as someone else posted (small draw), and put an 18v (nominal) charger
on the 3 batteries tapped for the lift.  It doesn't have to be a big
charger,
2-3amps max should do fine to balance out the lift usage, unless you
constantly use the lift.  It doesn't have to be highly efficient, since 
it's
just providing 'equalizing' charging, the ET charger will do the bulk of
the charge.

Another idea I plan to experiment with... I have one of the Curtis 1505
24v nominal 20A continuous 80A 1min controllers that were used on
the EVWarrior bike.  I'm planning to hook it up in series with the lift
switch, tapping 24v of batteries instead of 18v.  Not only will it spread
the load to 4 batteries instead of a 'harder to charge' 3, but will give
me the ability to tailer the lift speed to some degree, instead of it
operating
at about 19v (+- 1v depending on charge state), it can then be operated
at a selected speed by twisting a throttle control - say to lift the mower
deck or plow blade quicker.  Otherwise the lift would operate the same,
via the existing switch.  Bought it complete with bike harness (all the
goodies necessary to run it are included) for $40.  It includes a on-off
switch, thumb operated speed controller (0-5k pot), horn, 24v to 12v
dc/dc to run the headlights, a information display consisting of a power
on LED, an emergency flasher LED (flashes all 12v lights, controlled by
a separate switch), and 2 10segment LED displays that show voltage
and power consumption, and a remote key fob to lock out the controller
if you like. For $50 total you can get that plus headlight, taillight, side
mirrors
with integrated turn signals, etc.  Industrial Liquidators is selling them
on
their website (for more) and on ebay for the amounts shown.  Just search
for EV Warrior on ebay.  My son and I have already put one full harness
(including all the lights, horn, etc) on his PowerWheels vehicle.  Good 
deal
for the price.

I also purchased on Ebay from the same outfit a couple of Todd 40Amp
power supplies (switchable from 13.2v and 14.4v) that run off A/C to
be used as 'fast chargers' and balancers.  I'll be getting rid of my old
6v's (8 years on them now, but still more than I need, but 1 leaks at
the top case seal) - actually I'll keep them around for a while for home
power backup.  And I'm putting in 3 SBS-60 Hawkers to run the machine.
The Todd's will keep them balanced, and the lift will run off 2 of them via
the controller.  The Todds cost me about $50 each, the Hawkers were
$40 each, so for $150 + $120 + $40 I'm getting a lighter, cleaner power
source (they are sealed AGM's not floodeds that wreck the paint) that
I can fast charge (Hawker's like fast charging) in the event I need to plow
more than just my driveway once - by the time the driveway needs clearing
again in a big long snowfall the Hawkers can be topped off for another
pass.  They will be plenty for mowing, especially after losing 230lbs of
weight.  If I need more weight for plowing, I'll fill up the rear battery
box with weight, otherwise it can serve as a tool/etc compartment.  With
the motor, transaxle, and me over the back there's plenty of weight back
there for mowing. The next stage modification will be to consider replacing
the current ET controller with a 48v controller, and add a 4th Hawker and
Todd (bought them already, too), and possible a matching motor (EVParts.com
sells a nice match for good price).

I'll be sure to post about the results as I complete them, and I'll
construct a
website to document it.  My first 'public consumption' website covers my
Toyota Prius modification consisting of a trunk-installed 1kw inverter.
See http://www.geocities.com/priusmods/PriusMods.html for a (not yet
complete) example of how I intend to document it.

> A more economical way to monitor individual batteries would be 6 LED's,
> each hooked up to one battery with a zener diode with the values chosen
> such that the LED goes out when the battery voltage drops below say
> 5.3(?) volts.  This would give you a quick visual indication of which
> battery was weakest by which light started dimming first under load (and
> would also tell you when to back off on the "gas" pedal...). So maybe an
> e-meter in the first meter hole, and a little panel with 6 LED's
> arranged in the same pattern as the batteries are installed in the
> second hole.

Lee Hart has for sale a low cost item called a Batt-Bridge.  It has a 
single
light that turns on when a single cell anywhere in the pack goes 'dead'. It
doesn't tell you where other than which half of the pack it's in, but it's
all
you need when you are driving - stop pulling amps now or you're going
to hurt a battery.

-Chris